Crystal rectifier converter



May 3, 1949.

J. B. ATwooD ET Al. 2,469,222

CRYSTAL RECTIFIER CONVERTER Filed DGO. l, 1943 JoH/v A rwoo,

,BERT/BAM TBEVOP/ ATTORNEY Patented May 3, 1949 UNITED STATES PATENT OFFICE CRYSTAL RECTIFIER CONVERTER Application December 1, 1943, Serial No. 512,442

(Cl. Z50-20) Claims.

The present invention relates to converters, and more particularly to converters for ultra-high frequency super-heterodyne receivers.

An object of the present invention is the provision of a converter circuit for an ultra-high frequency super-heterodyne receiver.

Another object of the present invention is the improvement of crystal rectifier converter circuits.

Another object of the present invention is the provision of a balanced converter circuit for ultra-high frequency super-heterodyne receivers.

A further object of the present invention is the provision of a balanced converter arrangement having a low degree of coupling between the oscillator and signal circuits.

A further object of the present invention is the reduction of oscillator radiation into the antenna circuit of a super-heterodyne receiver.

Still a further object of the present invention is to prevent the loss of incoming signal energy in the oscillator circuit of a super-heterodyne receiver.

The foregoing objects and others which may appear from the followingdetailed description are obtained in accordance with the principles of the present invention by the provision of a crystal retcier converter arranged in the form of a balanced circuit whereby little, if any, of the applied oscillator voltage is transferred to the antenna circuit. The conversion or mixing action in the circuit is performed by a pair of crystal rectiiiers arranged in a push-pull relationship. Preferably all of the resonant circuit elements in the converter circuit are constituted by line sections having uniformly distributed constants. Means are provided for entirely shielding the converter circuit, and further means are provided for matching the impedance of the signal input circuit to the imdance of the transmission line connected thereto.

The invention will be more fully understood by reference to the following detailed description, which is accompanied by a drawing in which:

Figure 1 is an electrically equivalent circuit of the present invention which utilizes lumped circuit constants, and which is useful in understanding the operation of the invention; while lIigure 2 illustrates in detailed cross-section an embodiment of the invention.

In Figure l, there is illustrated a tuned circuit I including an inductance 2 and a tuning capacity 3. Across the ends of the tuned circuit I are connected a pair of crystal rectiers 4 and 5 arranged in a push-pull relationship. Oscillatory wave energy from any desired source such as a local oscillator .is coupled into tuned circuit I by a coup-ling link B. Incoming signal energy such as from antenna 1 is applied to the system across a variably tapped inductance 8 connected between a center tap on coil 2 and a point of zero reference potential such as that indicated by the ground symbol.

The best frequency resulting from the mixture of the oscillatory wave energy applied to the circuit through coupling link S and the incoming signal energy from antenna I is abstracted from the circuit through the medium of an output circuit 9 which is connected to the following intermediate frequency amplier (not shown).

It will be noted that the coupling inductance 8 for the antenna circuit is mounted in the system at a point of substantially zero potential with respect to ground for energy from the oscillator circuit. Therefore, none of this energy is supplied to the antenna 1. Similarly, substantially none of the signal energy from antenna I is coupled into the oscillator link 6 due to the opposing phase relationships of the signal current through inductance 2.

The actual mechanical construction of the converter of the present invention is shown in detail in Figure 2, wherein the tuned circuit I of Figure 1 is constituted by a resonant line structure lil. The resonant line structure includes a pair of parallel conductors II and I2 insulatingly supported within an outer casing I3 by insulators Il. The insulating supports are preferably of some low loss material such as polystyrene or methyl-methacrylate. A conductive wall I4, electrically a part of casing I3, is mounted between rods I I and I2 so that each of the rods I I and I2, together with the surrounding conductive wall structure, constitutes a coaxial line section. Rods II and I2 are connected together at each end with adjustable shorting bars I5, I5i These bars may be slid along the length of rods I I and l2 to such position that the total included length between the shorting bars is of the order o1"- three quarters of lthe operating wavelength. Clamping screws I6 are provided at each end of the shorting bars I5, 4I 5 to rigidly clamp the shorting bars in position.

The oscillator input is coupled tothe tuned circuit lll by means of a coaxial line fitting I8 including an outer threaded shell I9 connected to casing I3, and an inner conductor 20 coupled to rod I2 of the resonant circuit I0. Conductor 2.0 is maintained in coaxial .alignment with threaded sleeve I9 by means of insulating Washers 2I. The

point of connection of conductor 20 to rod I2 is preferably spaced a distance equal to one quarter of the operating Wavelength from one end of shorting bar I5.

The signal input to the converter from an antenna (not shown) is applied to coaxial line fitting 22 which is similarly constructed to fitting I 8. The inner conductor 20 of coaxial line iitting 22 carries on its inner end a spring 23 bearing against stub 24 of a quarter wave resonant circuit 25. The signal input coaxial fitting 22 is mounted on a plate 26 so arranged that the entire fitting may be slid up and down, thus changing the effective size of the coupling loop constituted by inner conductor 20, spring 23 and stub 24.

Tuning of the quarter wave resonant circuit 25 may be accomplished by providing a rod 30 arranged for slidable operation within stub 24. Preferably the rod 30 is so arranged, as by a slot and key construction 3l, that it will only slide and not turn within stub 24. Rod 30 is hollow and threaded on its inside for threaded engagement with rod 32. Thus, as rod 32 is rotated by means of knurled knob 33, the effective length of rod 30 protruding from stub 24 may be adjusted to the desired quarter wave relationship.

The resonant line structure I@ is coupled to the quarter wave resonant circuit 25 by means of a wire 34 connected to shorting bar I5 and to stub 24 at a predetermined point. Wire 34 passes through an aperture in the end wall of the casing I3 surrounding the resonant line structure IB, and is maintained in insulated relationship thereto by an insulating button 35.

The quater wavelength circuit 25 between the antenna input 22 and the converter acts as an impedance matching device, the antenna match being adjustable to accommodate various antennas, etc. The connection 34 from circuit 25 to the tuned line I is fixed at a predetermined point on stub 24 since the impedance of the line sections is substantially constant over a reasonable operating range of frequencies.

The crystal rectiiiers 4B and 4I are arranged to plug in at one end to spring clips 42 and 43 carried by rods II and I2. Electrical contact to the otherend at each of the rectifiers 4i) and 4I is provided by springs 45 carried by a conductiveV plate 46. Conductive plate 45 is insulated from the conductive body of casing I3 by means of a thin strip of insulation `ll which may be of mica, and by means of insulating washers 4l under the heads of the securing screws. Thus, a by-pass condenser for signal frequencies is provided between the effective cathode of each of the crystal rectifiers and the grounded casing I3. This by-pass capacity is, however, too small to substantially attenuate the intermediate frequency output of the converter which is conducted by means of coaxial lines 48 and 49 to the desired intermediate frequency coupling circuits.

In order to entirely shield the rectiers 40 and 4I from outside influences, shielding caps 5B and I are provided. These are designed to thread onto threaded mounts 52 and 53 carried on the casing I3. In order to insure that the crystal rectiiers 40 and 4I are maintained in position in spite of vibration and so forth, springs 54 are centrally mounted within caps 50 and 5I and arranged to bear on the outer ends of crystal rectiers 40 and 4I. In order to prevent shorting of the intermediate frequency output, springs 54 are insulated from caps 5I] and 5I by means of interposed insulating blocks 55 and 56.

It will be noted that the distance from the oscillator input tapping point 20 to crystal tap 43 is A/4, where is the operating wavelength. .The distance from 20 to 4,2 is 3 \/4. Therefore, these points are 3A/4-A/42x/2, or 180 apart, and hence are in push-pull relationship. That 34 is a center tap necessarily follows from the arrangement such that distances 34--42, 34-43 are each M4.

Since at the contemplated operating frequencies the difference between the oscillator and signal frequencies is so slight as to be a second order effect, either frequency may be used in calculating the line lengths to .be used.

While we have illustrated a particular embodiment of the present invention, it should be clearly understood that it is not limited thereto since many modifications may be made in the several elements employed and in their arrangement, and it is therefore contemplated -by the appended claims to cover any such modifications as fall within the spirit and scope of the invention.

Having now described our invention, what we claim as new and desire to have protected by Letters Patent is:

1. A converter circuit including a pair of parallel coaxial line sections each including an inner conductor and a surrounding outer shell, said inner conductors .being connected together at each end, means for applying wave energy of one frequency across said line sections in a parallel relationship, means for applying wave energy of another frequency to said line sections in a pushpull relationship, and a pair of rectifier elements connected in a symmetrical arrangement from opposing pionts on said inner conductors to an output circuit.

2. A converter circuit including a pair of par-r allel coaxial line sections each including an inner conductor and a surrounding outer shell, said inner conductors being connected together at each end, means for applying wave energy of one Y frequency across said line sections in a parallel relationship, means for applying wave energy of another frequency to said line sections in a pushpull relationship, a pair of crystal detectors each having a terminal connected in a symmetrical arrangement to opposing points on said inner conductors, bypass condensers connected from each of the other terminals of said crystal detectors to a point of zero reference potential, and an output circuit connected across said other terminals.

3. A converter circuit including a -pair of parallel coaxial line sections each including an inner conductor and a surrounding outer shell, said inner conductors being connected together at each end, means for applying wave energy of one frequency across said line sections at one end in a parallel relationship, means for applying wave energy of another frequency to said line sections in a push-pull relationship, and a pair of rectifier elements connected in a symmetrical arrangement from intermediate high potential points on said inner conductors to a balanced output circuit.

4. A converter circuit including a pair of parallel coaxial line sections each including an inner conductor and a surrounding outer shell, said inner conductors being connected together at each end, each of said conductors having a length equal to three quarters of the operating wavelength, means for applying wave energy of one frequency across said line sections at one end in a parallel relationship, means .for applying wave energy of another frequency to one of.

said line sections at a distance of one quarter Wavelength from the other end whereby said conductors are energized in a push-pull relationship, and a pair of crystal detectors each having a terminal connected in a symmetrical arrangement to one o1" said inner conductors at a distance of one quarter wave length from said one end, other terminals of said detectors being connected to an output circuit.

5. A converter circuit including a pair of parallel coaxial line sections each including an inner conductor and a surrounding outer shell, said inner conductors being connected together at each end, means for applying Wave energy of one frequency across said line sections at one end in a parallel relationship, said means including an impedance matching network connected between the source of said wave energy and said line sections, means for applying Wave energy of another frequency to said line sections in a pushpull relationship, and a pair of rectiiier elements connected in a symmetrical arrangement from intermediate high potential points on said inner conductors to a 'balanced output circuit.

6. A converter circuit including an elongated conductive housing having a longitudinal partition therein, an inner conductor in each chamber of said housing, said inner conductors being connected together at each end, means for applying wave energy of one frequency between said inner conductors and said housing at one end in a parallel relationship, said means including an impedance matching network connected between the source of said wave energy and said conductors, means for applying Wave energy of another frequency to one of said conductors at such distance from one end that said conductors are energized in a push-pull relationship, and a pair of rectifier elements connected in a symmetrical arrangement from intermediate high potential points on said inner conductors to a balanced output circuit.

7. A converter circuit including an elongated conductive housing having a longitudinal partition therein, an inner conductor in each chamber of said housing, said inner conductors being connected together at each end, means for applying wave energy of one frequency between said inner conductors and said housing at one end in a parallel relationship, said means including Van impedance matching network connected between the source of said wave energy and said conductors, means for applying wave energy of another frequency to one of said conductors at such distance from one end that said conductors are energized in a push-pull relationship, a pair of detectors extending through the Wall of said housing each having a terminal connected to one of said inner conductors at a distance of one quarter of the operating wave length from said one end, connections from the outer ends of each of said detectors to an output circuit, and conductive shield caps over each of said outer ends.

8. A converter circuit including an elongated conductive housing having a longitudinal partition therein, an inner conductor in each chamber of said housing, said inner conductors being connected at each end, means for applying wave energy of one frequency between said inner 'conductors and said housing at one end in a parallel relationship, said means including an impedance matching network including a quarter wave resonant line section having an outer shell and a variable length inner conductor, a connection from a xed point on said inner conductor to 6 one end of the inner conductors, a connection from the source of said wave energy to an adjustable point on said variable length inner conductor, means for applying Wave energy of another frequency to one of said conductors at such distance from one end that said conductors are energized in a push-pull relationship, a pair of detectors extending through the wall of said housing each having a terminal connected to one of said inner conductors at a distance of one quarter of the operating wave length from said one end, connections from the outer ends of each of said detectors to an output circuit and conductive shield caps over each of said outer ends.

9. A converter circuit including a pair of parallel coaxial line sections each including an inner `conductor and a surrounding outer shell, said inner conductors 'being connected together at each end, means for applying wave energy of one frequency across said line sections at one end in a parallel relationship, said means including an impedance matching network including a quarter wave resonant line section having an outer shell and a variable length inner conductor, a connection from a Xed point on said inner vconductor to one end of the inner conductors of said pair of line sections, a connection from the source of said wave energy to an adjustable point on said inner conductor, means for so applying wave energy of another frequency to an intermediate point on said line sections that said energy appears on said line sections in an opposing phase relationship, a pair of rectier elements connected in a symmetrical arrangement from intermediate high potential points on said inner conductors to a balanced output circuit, said output circuit being so bypassed as to be responsive only to frequencies no greater than the difference between the frequencies of said applied wave energies.

10. A converter circuit including a pair of parallel conductors connected together at each end and an outer casing enclosing said conductors, a conductive wall between said conductors 1 and connected to said outer casing, means for applying wave energy of one frequency between said line conductors and said outei1 casing, means for applying wave energy of another frequency to said line conductors in a push-pull relationship and rectifying means connected in symmetrical relationship from corresponding high potential points on said conductors to an output circuit.

JOHN B. ATWOOD. BERTRAM TREVOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,418,285 Carson June 6, 1922 2,097,514 Chaffee Nov. 2, 1937 2,106,776 Trevor et al Feb. 1, 1938 2,136,606 Bendel Nov. 15, 1938 2,142,159 Southworth et al. Jan. 3, 1939 2,261,879 Higgins Nov. 4, 1941 2,285,372 Strutt et al. June 2, 1942 2,216,964 Stepp Oct. 8, 1944 2,410,122 Mercer Oct. 29, 1946 OTHER REFERENCES Ser. No. 380,368, Dallenba-ch et al. (A. P. C), published June 8, 1943. 

